Gerald Koudelka is Professor and Chair of Biological Sciences at the University at Buffalo. His lab conducts research into the mechanisms of DNA sequence recognition and the evolution of bacteriophage-encoded exotoxins. He holds a Ph.D. from the University at Buffalo.

If you’ve ever taken a dip to cool off in a lake or creek, you may have paused for a moment to ponder whether the water was safe. One of the biggest health risks for recreational swimmers is E. coli, a bacteria that can cause diarrhea and vomiting. Extreme cases can lead to death, and authorities often shut down beaches when E. coli levels are high. These types of closures may make sense at first glance, but the real story is more nuanced.

There are many different types of E. coli, and most are actually harmless. However, strains that produce a poison called Shiga toxin can make people sick. The problem with many current water quality tests is that they measure only the total number of E. coli in a river or lake. These tests do not discriminate between the various types of E. coli. My latest research adds to evidence suggesting that this is a bad way to capture risks for swimmers.

In a recent study, my partners and I discovered that Shiga toxin-producing E. coli survived longer in samples of lake water than E. coli that didn’t produce the toxin. One particularly nasty strain persisted for 48 hours before declining. Our evidence suggests the dangerous strains performed better because Shiga toxin helps them fend off aquatic predators like protists — small, single-celled creatures that feed on bacteria.

Our findings provide one possible explanation for why overall E. coli populations don’t always correlate with levels of dangerous, toxin-producing E. coli in the water. It’s possible to have high E. coli levels but have most of that E. coli be harmless. Conversely, it’s also possible to have low E. coli levels overall, but high levels of the nastiest strains. If you’re tests are too general, you could miss the danger.

Production support for the Academic Minute comes from Newman’s Own, giving all profits to charity and pursuing the common good for over 30 years, and from Mount Holyoke College.

In today’s Academic Minute, Dr. Stephen Mucher of Bard College explains the motivations behind the first teacher observations of the nineteenth century.

Stephen Mucher is an assistant professor of history and education at Bard College. His teaching and research interests include history education, the history of education, and the development of historical thinking processes in adolescents. He earned his Ph.D. at the University of Michigan.